linux-kernel - Re: [v5][PATCH 5/6] mm: vmscan: batch shrink_page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20130604065930.GA26129@blaptop>
Date:	Tue, 4 Jun 2013 15:59:30 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mgorman@...e.de,
	tim.c.chen@...ux.intel.com
Subject: Re: [v5][PATCH 5/6] mm: vmscan: batch shrink_page_list() locking
 operations

On Mon, Jun 03, 2013 at 11:10:02PM -0700, Dave Hansen wrote:
> On 06/03/2013 10:01 PM, Minchan Kim wrote:
> >> > +static int __remove_mapping_batch(struct list_head *remove_list,
> >> > +				  struct list_head *ret_pages,
> >> > +				  struct list_head *free_pages)
> >> > +{
> >> > +	int nr_reclaimed = 0;
> >> > +	struct address_space *mapping;
> >> > +	struct page *page;
> >> > +	LIST_HEAD(need_free_mapping);
> >> > +
> >> > +	while (!list_empty(remove_list)) {
> ...
> >> > +		if (!__remove_mapping(mapping, page)) {
> >> > +			unlock_page(page);
> >> > +			list_add(&page->lru, ret_pages);
> >> > +			continue;
> >> > +		}
> >> > +		list_add(&page->lru, &need_free_mapping);
> ...
> > +	spin_unlock_irq(&mapping->tree_lock);
> > +	while (!list_empty(&need_free_mapping)) {...
> > +		list_move(&page->list, free_pages);
> > +		mapping_release_page(mapping, page);
> > +	}
> > Why do we need new lru list instead of using @free_pages?
> 
> I actually tried using @free_pages at first.  The problem is that we
> need to call mapping_release_page() without the radix tree lock held so
> we can not do it in the first while() loop.
> 
> 'free_pages' is a list created up in shrink_page_list().  There can be
> several calls to __remove_mapping_batch() for each call to
> shrink_page_list().

I missed that point.

> 
> 'need_free_mapping' lets us temporarily differentiate the pages that we
> need to call mapping_release_page()/unlock_page() on versus the ones on
> 'free_pages' which have already had that done.
> 

Right.

> We could theoretically delay _all_ of the
> release_mapping_page()/unlock_page() operations until the _entire_
> shrink_page_list() operation is done, but doing this really helps with

                                        maybe you mean
                                        but doing this doesn't really helps
> lock_page() latency.
> 
> Does that make sense?

If so, It does make sense.
Thanks for pointing me out.

> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@...ck.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>

-- 
Kind regards,
Minchan Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/